The field of the invention is water craft and the invention relates more particularly to devices to protect the propellers of water craft. Various shrouds have been placed around propellers for various reasons in the prior art. U.S. Pat. No. 123,629 shows a hollow cylindrical device used solely to steer a motorboat with an inboard motor.
A propeller assembly having an annular rim 46 is shown in U.S. Pat. No. 3,377,978. The propeller is driven by contact with a pneumatic tire.
A propeller mount for ice breakers is shown in U.S. Pat. No. 4,428,735. The propellers of the ice breaker are protected by a shield 11.
The U.S. Pat. No. 4,680,017 shows a propeller guard on an outboard motor. The propeller guard is held to the motor by a shield which goes over the cavitation plate.
The U.S. Pat. No. 4,746,314 shows a combined propulsion and steering system for a boat with an inboard engine. The Levi device has an arch-like deflector tunnel over the propeller.
Lastly, an article at Page 96 of the March 1992 issue of Boating World describes an outboard motor having a "Kort nozzle" held over the propeller for the purpose of increasing boat speed, particularly for heavy boats at slow speeds.
The propellers of motorboats are often damaged by contact with sandbars, shallow bottoms, rocks and debris. This is especially true for the propellers of houseboats since houseboats are typically piloted from the front of the houseboat where it is difficult to see the depth of the water under the propeller. It is also desirable to increase the efficiency of a propeller, particularly at low speeds.